Biochemical aspects of olfactory mechanisms

Electron microscopic examination of intact olfactory epithelia in different animals yielded the same pattern of morphological organisation of the cellular organelles. Attempts have been made to isolate cilia from the primary olfactory neurons in order to study the molecular mechanisms involved in olfaction. The results indicated that the purity and quantity of the ciliary preparation obtained by current membrane fractionation methods was not suitable for biochemical investigations. Also ciliated columnar respiratory cells have been found in the olfactory mucosa of sheep. This feature presents difficulties for future neuronal membrane isolation attempts. Two basic problems in olfaction, coding and transduction have also been studied in this thesis. Chemical modification methods have been employed to study the coding mechanism at the peripheral level in the frog. With a variety of group specific protein reagents, proteolytic enzymes and photoaffinity odorants, it has been possible to specifically modify olfactory receptors. The non-penetrant sulfhydryl reagent, mersalyl irreversibly inhibited the EOG responses to odorants. This effect was found to be prevented by n-amyl acetate. Application of this odorant in solution before, during and after the treatment of the mucosa with mersalyl resulted not only in protection of the responses to n-amyl acetate, but also to other odorants as well. Responses to some odorants did not show any recovery providing evidence for the occurrence of different receptor sites. To investigate the possible involvement of cAMP in the olfactory transduction mechanism, a number of chemicals were applied to the frog's olfactory mucosa. Phosphodiesterase inhibitors and membrane- permeable cyclic AMP derivatives decreased the EOG responses. One contribution of this thesis to the field of olfaction has been to show that olfaction has biochemical features common to other receptor systems